1. Field of the Invention
The present invention relates to a rotary type electric shaver and more particularly to installation positions of an outer cutter and an inner cutter of an electric rotary shaver.
2. Prior Art
FIG. 7 shows an outer cutter unit in a conventional rotary type electric shaver.
The rotary type electric shaver of FIG. 7 is a so-called three-headed electric shaver. In this shaver, three outer cutters 10 each in a circular ring shape are disposed in an outer cutter frame 12, and the centers of three outer cutters are arranged so as to coincide with the vertices of an equilateral triangle. Slit holes 11 for the introduction of hair are formed in the outer cutters 10; and numerous number of such slit holes 11 are oriented in the circumferential direction of each of the outer cutters 10.
FIG. 8 shows the internal construction of the outer cutter unit that includes the outer cutter 10. In FIG. 8, only one outer cutter is shown. The outer cutter 10 is formed in a shape of a cap, the cutting portion 10a that comes into contact with the skin is flat, and slit holes 11 are formed through this cutting portion 10a. 
Each inner cutter 20 includes a plurality of inner cutter blades 21 that are formed in an upright position around the circumference of an inner cutter blade supporting body 22 which is in the shape of a circular disk. The tip end portions of the inner cutter blades 21 that make sliding contact with the interior surface of the corresponding cutting portion 10a of the outer cutter 10 constitute cutters that cut hair.
The inner cutter blade supporting body 22 is provided at its center with an engaging hole 24 that engages with a drive shaft which is rotationally driven by a driving motor installed in the main body of the electric shaver. As a result of the drive shaft engaging with this engaging hole 24, the inner cutter 20 is rotationally driven as a unit with the drive shaft and acts in conjunction with the outer cutter 10 to cut hair introduced into the interior of the outer cutter 10 via the slit holes 11.
As described above, in a rotary type electric shaver, shaving is accomplished by causing the inner cutter 20 to rotate interior of the outer cutter 10 so that hair introduced into the outer cutter 10 is cut by the inner cutter 20 and outer cutter 10. Accordingly, in conventional rotary type electric shavers, the center of the outer cutter 10 and the center of the inner cutter 20 are coincide, thus being coaxial with each other, and the inner cutter 20 is rotationally driven in a coaxial fashion with the outer cutter 10. In FIG. 8, Ds indicate the separating gaps between the outer circumferential side surface of the outer cutter 10 and the position of the outside surface of the inner cutter 20 (or position of the outside surface of the inner cutter blade 21). In the conventional rotary type electric shavers, since the outer cutter 10 and inner cutter 20 are provided coaxially, this gap D is constant around the entire circumference of the outer cutter 10.
Generally, in rotary type electric shavers, hair introduced into the interior of the outer cutter 10 through the slit holes 11 of the outer cutter 10 is cut by the inner cutter 20 and outer cutter 10. During shaving, the skin enters the interior of the outer cutter via the slit holes 11 of the outer cutter 10, especially via the portions of the slit holes 11 on the outer portion side of the outer cutter 10. Deep shaving is made possible since the skin thus enters into the slit holes 11. However, if the gap D shown in FIG. 8 is narrow, the skin that enters the outer cutter 10 is injured by the inner cutters 20 (i.e., shaver burn occurs). On the other hand, if the gap D is wide, though there is no problem of the skin being injured by the inner cutter 20, deep shaving becomes impossible.
Furthermore, the amount of protrusion of the skin into the interior of the outer cutter 10 also varies according to the softness of the skin. As a result, in cases where the cheeks are shaved, the skin tends not to enter the slit holes 11, thus making deep shaving difficult, while in cases in which areas where the skin is soft such as the jaw and an area under the jaw are shaved, the skin readily enters the slit holes 11 and is easily injured.